Nephi knows that records serve multiple purposes. The first is the preservation of "language", perhaps in the meaning of culture and knowledge of God. Another is the historical function of recording the works of the leaders of men. Yet another is a record for the purpose of convincing those who follow of the goodness of God. Nephi clearly dedicates the small plates to this last task.
It is interesting, in light of Nephi's declaration that he did not want to repeat the record of Lehi, nor the genealogies of the brass plates, that he did include large sections of Isaiah in his narrative. Like the genealogies of Joseph, Isaiah was material available on the brass plates (we assume from the fact that they were copied into Nephi's record, and the brass plates were the most logical source). Clearly Nephi felt that those copied sections of Isaiah more completely furthered his goal of teaching things pleasing to God than did the genealogies.